CN117990641A - Method for synchronously measuring trace gas leakage of natural gas based on mid-infrared absorption spectrum - Google Patents
Method for synchronously measuring trace gas leakage of natural gas based on mid-infrared absorption spectrum Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 266
- 239000007789 gas Substances 0.000 title claims abstract description 94
- 239000003345 natural gas Substances 0.000 title claims abstract description 45
- 238000000034 method Methods 0.000 title claims abstract description 35
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- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 claims abstract description 65
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- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 claims description 6
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- NAXKFVIRJICPAO-LHNWDKRHSA-N [(1R,3S,4R,6R,7R,9S,10S,12R,13S,15S,16R,18S,19S,21S,22S,24S,25S,27S,28R,30R,31R,33S,34S,36R,37R,39R,40S,42R,44R,46S,48S,50R,52S,54S,56S)-46,48,50,52,54,56-hexakis(hydroxymethyl)-2,8,14,20,26,32,38,43,45,47,49,51,53,55-tetradecaoxa-5,11,17,23,29,35,41-heptathiapentadecacyclo[37.3.2.23,7.29,13.215,19.221,25.227,31.233,37.04,6.010,12.016,18.022,24.028,30.034,36.040,42]hexapentacontan-44-yl]methanol Chemical compound OC[C@H]1O[C@H]2O[C@H]3[C@H](CO)O[C@H](O[C@H]4[C@H](CO)O[C@H](O[C@@H]5[C@@H](CO)O[C@H](O[C@H]6[C@H](CO)O[C@H](O[C@H]7[C@H](CO)O[C@@H](O[C@H]8[C@H](CO)O[C@@H](O[C@@H]1[C@@H]1S[C@@H]21)[C@@H]1S[C@H]81)[C@H]1S[C@@H]71)[C@H]1S[C@H]61)[C@H]1S[C@@H]51)[C@H]1S[C@@H]41)[C@H]1S[C@H]31 NAXKFVIRJICPAO-LHNWDKRHSA-N 0.000 description 2
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Abstract
The invention relates to the technical field of natural gas leakage, and discloses a method for synchronously measuring trace gas of natural gas leakage based on an intermediate infrared absorption spectrum. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum covers a 2989.033cm ‑1、2988.932cm‑1、2988.795cm‑1 methane absorption line and a 2986.705cm ‑1 ethane absorption line, a natural gas leakage source is simulated through mixed gas of 1% methane and 0.1% ethane (the residual gas is N 2), a mobile monitoring experiment is carried out, the measurement result shows that the methane and the ethane have strong linear correlation, the pearson correlation coefficient is 0.999133, the method is different from other methane sources such as methane, and a reliable basis is provided for distinguishing the natural gas leakage.
Description
Technical Field
The invention relates to the technical field of natural gas leakage detection, in particular to a method for synchronously measuring trace gas of natural gas leakage based on a mid-infrared absorption spectrum.
Background
In recent years, with the continuous increase of global energy consumption and continuous adjustment of energy structures, the ratio of natural gas in the energy structures is increasingly increased, and the domestic demand for natural gas is also increasingly increased, so that natural gas is becoming one of the main energy sources of public facilities and resident lives in large, medium and small cities in China due to the advantages of high heat value, energy conservation, environmental protection, economy, practicability and the like. With the wide use of natural gas, a large number of town gas pipe networks are newly built and operated, and the risk of town gas leakage is continuously increased, if the natural gas can not be detected and found in time, disastrous accidents such as combustion, explosion and the like can be possibly caused, and the natural gas leakage can not only cause environmental pollution, resource waste and facility damage, but also endanger the life and property safety of people.
Therefore, whether to effectively develop gas leakage detection becomes a critical problem to be solved in the safety operation of town gas pipe network systems, and in order to accurately detect natural gas leakage, the selection of a detection technology is important. Compared with non-optical detection technologies such as a gas-sensitive method, a catalytic combustion method, an electrochemical method and the like, the infrared absorption spectrum gas detection technology has the advantages of high precision, quick response, good selectivity, small drift, real-time in-situ detection and the like, and is widely applied to the field of gas leakage detection. Mcha et al develop a set of vehicle-mounted mobile methane sensor for natural gas leakage based on a methane spectral line of 1.651 mu m, wherein the detection sensitivity is 10-15 ppbv, and the vehicle-mounted mobile measurement is about 30 ppbv; zhang Ke et al designed a gas concentration detection device in a complex environment based on infrared absorption spectrum technology by utilizing a 3.312 mu m wave band quantum cascade laser, and compared with a chemical catalysis methane gas measuring instrument, the gas concentration detection device has higher measurement precision and stability. Huang Sailin a methane concentration detection system based on a continuous wavelength quantum cascade laser is designed, a second harmonic peak method is used for realizing methane concentration measurement, and when the integration time is 10s, the detection lower limit of the system is 7.19ppmv. She Weilin et al built a set of ethane sensors with a 220ml multipass cell and interband cascade laser with measurement accuracy up to 10-9 orders of magnitude and placed in a gas station for field experiments to detect significant changes in ethane concentration. Ge et al developed a mid-infrared sensor for detecting methane by using the absorption line of methane molecules at 3038.5cm < -1 > as a target spectral line, and detected the lower limit by an Allan analysis of variance system; and the obtained concentration data and gas image data are utilized to realize natural gas leakage monitoring by combining an intelligent algorithm.
In short, researchers have studied the concentration detection of methane and ethane gases, but only single concentration detection of methane/ethane gases is difficult to effectively identify the gas leakage position and is easily interfered by other methane sources.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum, which has the advantages of accurate identification and the like and solves the technical problems.
In order to achieve the above purpose, the present invention provides the following technical solutions: the method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum comprises the following steps of:
s1, selecting and measuring the absorption spectrum of methane and ethane in natural gas;
s2, constructing a methane and ethane detection system;
s3, analyzing the performance of the detection system;
S4, detecting natural gas leakage.
As a preferred embodiment of the present invention, the specific value determining process of the absorption spectrum in the step S1 is as follows:
s1.1, determining an absorption line of 2ppm methane, 80ppb ethane and 2% water under different intensity pressure conditions;
s1.2, adopting a cascade laser between intermediate infrared continuous wavelength bands as a light source, and determining an absorption spectrum line;
s1.3, drawing images of methane, ethane and water spectral lines, and determining the optimal absorption spectral line.
As the preferable technical scheme of the invention, the detection system comprises a middle infrared laser, a long-optical-path gas cell, a middle infrared photoelectric detector, a data acquisition card, a semi-transparent semi-reflective mirror and an etalon, wherein the laser comprises a current driving module and a temperature control module.
As a preferable technical scheme of the invention, the system constructed in the step S2 comprises the following specific working steps:
s2.1, performing current tuning on the laser through a current driving module, setting the center temperature of the laser by using a temperature control module, covering the methane and ethane absorption spectrum lines selected in the step S1, and emitting laser;
s2.2, emitting laser by a laser, and dividing the laser into two beams by a half-mirror;
S2.3, one beam passes through the etalon and then reaches the detector to realize the conversion of the relative frequency and the time domain of the light emitted by the laser, and the other beam of laser enters the long-path gas cell after being collimated, and the multiple reflection can reach 13m of effective optical path length and is absorbed by gas molecules to be detected;
s2.4, the mid-infrared photoelectric detector receives the transmitted light intensity after passing through the long-optical-path gas cell and converts the transmitted light intensity into a voltage signal;
S2.5, the data acquisition card processes the signals and calculates the gas concentration.
As a preferred embodiment of the present invention, the performance analysis in the step S3 includes the following steps:
s3.1, stability detection and lower limit detection;
s3.2, dynamic performance detection.
As a preferred embodiment of the present invention, the stability test and the lower limit test in step S3.1 are performed by continuously measuring gas samples having a volume fraction of 2ppm methane and 10 ppb ethane for 30 minutes, respectively.
As a preferred technical solution of the present invention, the dynamic performance detection in step S3.2 specifically includes the following steps:
s3.2.1 gas flow rate is controlled to be stabilized at 0.66L/min by using a gas distribution instrument
S3.2.2, pumping methane gas samples grouped by different volume fractions into a long-path gas cell by a vacuum pump respectively;
s3.2.3, sequentially increasing the minimum volume fraction to the maximum volume fraction at the same group interval, and sequentially decreasing the maximum volume fraction to the minimum volume fraction at the same group interval to complete continuous dynamic measurement;
s3.2.3, analyzing the error.
As a preferred technical solution of the present invention, the specific steps in the step S4 are as follows:
S4.1, continuously acquiring wind speed and wind direction data by using an anemograph, and carrying out surrounding running in a region with a leakage point;
S4.2, recording the position of the sensor in real time by using a global positioning system;
s4.3, recording methane and ethane concentration measurement values once per second, and synchronously calculating linear relation values of methane and ethane.
As a preferred embodiment of the present invention, the linear relation valueThe expression is as follows:
wherein/> Represents methane concentration measurements per second,/>Represents ethane concentration measurement per second,/>Represents the average value of methane concentration,/>The average value of ethane concentration is shown.
Compared with the prior art, the invention provides a method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum, which has the following beneficial effects:
1. According to the invention, by covering the 2989.033cm -1、2988.932cm-1、2988.795cm-1 methane absorption line and the 2986.705cm -1 ethane absorption line and carrying out a sensor dynamic detection experiment by preparing methane gas samples with different volume fractions, the detection result is basically consistent with the concentration of the gas samples, and the average response time of the sensor is 3.9s.
2. According to the invention, a natural gas leakage source is simulated through mixed gas (the residual gas is N 2) of 1% methane and 0.1% ethane, a mobile monitoring experiment is carried out, a measurement result shows that methane and ethane have strong linear correlation, a pearson correlation coefficient is 0.999133 which is different from other methane sources such as methane and the like, and a reliable basis is provided for distinguishing natural gas leakage.
Drawings
FIG. 1 is a schematic representation of absorption lines of 2ppmCH 4、80ppbC2H6 and 2% H 2 O at various pressures according to the present invention;
FIG. 2 is a schematic diagram of a construction system according to the present invention;
FIG. 3 is a graph of CH 4 concentration measurements versus time and a graph of CH 4 Allan variance according to the present invention;
FIG. 4 is a graph of concentration measurements versus time for C 2H6 and a graph of variance for C 2H6 Allan according to the present invention;
FIG. 5 is a graph showing the dynamic detection results of the system of the present invention for different concentrations of CH 4 gas;
FIG. 6 is a schematic flow chart of the present invention;
FIG. 7 is a linear relationship between CH 4 and C 2H6 concentration measurements according to the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The measuring principle of the invention is as follows:
The laser absorption spectrum measurement principle is based on Beer-Lambert law, when a beam of laser passes through a uniform gas medium to be measured, gas molecules to be measured can absorb photons with specific frequencies to generate energy level transition, and when different molecules are in energy level transition, photons with different frequencies need to be absorbed, so that the laser light intensity is attenuated to different degrees, and further different absorption spectrums are formed. Its absorptivity Available incident light intensity/>And transmitted light intensity/>To express: wherein P < atm > is the total pressure of the gas; x is the gas concentration, expressed in terms of volume ratio; l cm is the optical path length through the gas to be measured; TK is the gas temperature; s (T) [ cm -2/atm ] is the line intensity at temperature T; v cm -1 is the laser frequency; phi (v) is a linear function of the spectral line, using a Voigt line;
the absorption line intensity S (T) as a function of temperature can be expressed as: Wherein S (T 0)[cm-2/atm) is the absorption line intensity at the reference temperature T 0 (296K), and the size of the S can be obtained through an HITRAN database; Is the planck constant; c cm/s is the speed of light; e '' [ cm -1 ] is low-level energy; /(I) [ J/K ] is Boltzmann constant; /(I)[ Cm -1 ] is the transition center frequency. The last term in the formula is radiation excitation, and when the wavelength is less than 2.5 mu m and the temperature is lower than 2500K, the value approaches to 1 and can be ignored. Q (T) is a partitioning function, representing the ratio of the low-level particles to the total particles at temperature T. According to boltzmann's law of distribution, the intramolecular distribution function can be expressed as: wherein/> Represents the energy of the ith energy level, g i represents the degeneracy of the ith energy level. On the premise of meeting the measurement precision, the intramolecular distribution function can be rapidly calculated according to the polynomial approximation of 3 times of temperature segmentation: /(I)Wherein, the polynomial coefficients a, b, c, d of different gas molecules represent values in different temperature ranges.
The Pearson correlation coefficient is also called Pearson product-moment correlation coefficient, and is a linear correlation coefficient, and is marked as r, and is used for reflecting the linear correlation degree of the methane concentration X and the ethane concentration Y of two variables, wherein the r value is between-1 and 1, and the larger the absolute value is, the stronger the correlation is, and the more approximate the concentration change trend of the two variables is. The formula is as follows: wherein/> Represents methane concentration measurements per second,/>Represents ethane concentration measurement per second,/>Represents the average value of methane concentration,/>The average value of ethane concentration is shown.
Referring to fig. 1-7, the method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum comprises the following steps: s1, selecting and measuring the absorption spectrum of methane and ethane in natural gas;
Determining absorption lines of 2ppm of methane, 80ppb of ethane and 2% of water under different intensity pressure conditions, adopting a cascade laser between medium infrared continuous wavelength bands as a light source, determining the absorption lines, drawing methane, ethane and water line images, and determining the optimal absorption lines;
Methane absorption line 2989.033cm -1 (intensity 6.453X 10-20 cm/mol), 2988.932cm -1 (intensity 6.433X 10-20 cm/mol), 2988.795cm -1 (intensity 1.075X 10-19 cm/mol) and ethane absorption line 2986.705cm -1 (intensity 1.771X 10-20 cm/mol). At the absorption wavelength of the selected methane and ethane, the absorption spectrum line intensity of the water vapor is 1.102 multiplied by 10-22 cm/mol, which is 2-3 orders of magnitude smaller than that of the methane and ethane. FIG. 1 shows absorption lines for 2ppm methane, 80ppb ethane and 2% H 2 O at different pressures, where the gas pressures are 24kpa and 101.325kpa, respectively, the temperature T is 315K and the absorption length L is 13m. As can be seen from the figure, under standard atmospheric pressure, the absorption lines of methane and ethane are crossly interfered with the absorption lines of water, and the influence of the crossly interfered absorption lines of methane and ethane is larger; under the negative pressure of 24kpa, the collision broadening is reduced, the spectral line width is narrowed, the overlapping positions of the water vapor absorption spectral line and the methane and ethane absorption spectral line are less, the influence of the water vapor absorption spectral line is relatively flat, the influence of the water vapor absorption spectral line is negligible, and the interference of water vapor absorption on methane and ethane detection is effectively avoided;
s2, constructing a methane and ethane detection system;
The detection system comprises a middle infrared laser, a long-optical-path gas cell, a middle infrared photoelectric detector, a data acquisition card, a half-mirror and an etalon, wherein the laser comprises a current driving module and a temperature control module; the system comprises the following specific working steps:
The laser (Nanoplus, 3345 nm) carries out current tuning through a current driving module, the temperature control module is used for setting the central temperature of the laser, covering a methane absorption spectrum line 2989.033cm -1、2988.932cm-1、2988.795cm-1 and an ethane absorption spectrum line 2986.705cm -1, synchronously scanning methane and ethane absorption peaks, and outputting laser with required wavelength; the emergent laser is divided into two beams by a half-mirror, and one beam passes through an etalon and then reaches a detector, so that the conversion of the relative frequency and the time domain of the emergent laser is realized; the other laser beam enters a long-optical-path gas cell after being collimated, and the multiple reflection can reach 13m of effective optical path length and is absorbed by gas molecules to be detected; a mid-infrared photoelectric detector (VIGO PVI-4 TE) receives the transmitted light intensity after passing through the gas pool and converts the transmitted light intensity into a voltage signal; the analog-to-digital conversion module of the data acquisition card (NI MYDAQ) acquires the output signal of the detector and processes the signal so as to further calculate the gas concentration
S3, analyzing the performance of the detection system;
s3.1, stability detection and lower limit detection;
system stability is mainly affected by mechanical, electrical and optical noise, and stability and lower detection limits of the system are assessed by calculating the alan variance using long-term measurement data. Using this sensor, gas samples having a volume fraction of 2ppm methane, 10ppb ethane were each measured for 30 minutes continuously;
FIG. 3 is a graph of volume fraction 2ppm methane concentration measurements and their Allan variance. As can be seen from FIG. 3 (a), the fluctuation range of the methane volume fraction is 1.98ppm to 2.05ppm, the average concentration value of methane is 2.01ppm, and the average relative error is 0.5%. From FIG. 3 (b), the methane Allan variance at 1s for the system is 18.1ppb; when the integration time is 10s, the methane detection lower limit is 5.89ppb; at 327s, the lower methane detection limit of the system reaches the minimum value of 1.31ppb, and the system has good stability.
Fig. 4 is a graph of volume fraction 10ppb ethane concentration measurements and its allin variance. As is clear from FIG. 4 (a), the ethane measured value fluctuates between 8.18ppb and 12.86ppb, and the average concentration value is 10.18ppb and the average relative error is 1.8%. As can be seen from fig. 4 (b), when the integration time is 1s, the ethane detection lower limit is 1.06ppb; the lower limit of ethane detection at 11s of the system is 0.31ppb; at an integration time of 402s, the minimum detection lower limit can reach 0.02ppb.
S3.2, detecting dynamic performance;
During experiments, a mass flowmeter in a gas distribution instrument (HRHG 310,310) is used for controlling the gas flow rate to be stabilized at 0.66L/min, and a vacuum pump is used for pumping methane gas samples of 2ppm, 3ppm, 4ppm and 5ppm into a gas pool respectively for real-time detection. FIG. 5 is a continuous dynamic test run of the system with methane rising from 2ppm to 3ppm, 4ppm, 5ppm, and then falling from 5ppm to 4ppm, 3ppm, 2 ppm. From the graph, the methane concentration detection result is basically consistent with the concentration of the gas sample, the relative error is within 3%, and the measurement deviation is mainly caused by gas distribution error. Response time is generally defined as the time required for a change in the indication from 10% to 90% of the difference between its steady state concentration values, and is primarily influenced by the gas cell volume, gas sample flow rate, and processor data processing speed. As can be seen from the graph, the uplink response time is 4.1s, 3.7s and 3.5s, the downlink response time is 3.7s, 4.1s and 4.3s, and the average response time of the sensor is 3.9s
S4, detecting natural gas leakage;
Since the ratio of methane (volume fraction is about 90%) to ethane (volume fraction is about 9%) in natural gas is about 10:1, a mixed gas of 1% methane and 0.1% ethane (the residual gas is N 2) is taken as a natural gas leakage source, the mixed gas is placed at the right lower corner of an track and field, and a trolley carrying equipment such as a gas sensor and the like runs around a circle with the leakage source as the center and the radius of about 5m, so that a gas leakage movement detection test is carried out. In the experiment, wind speed and wind direction data are continuously collected by using an anemograph, and the position of a sensor is recorded in real time by using a Global Positioning System (GPS) module. Methane and ethane concentration measurements were recorded once per second and the methane and ethane linear relationship (i.e., pearson correlation) was calculated simultaneously, and fig. 7 is a linear relationship of methane and ethane concentration measurements. The concentration detected at the northwest of a leakage source is higher due to the on-site southeast wind, and the pearson correlation coefficient of the concentration measurement value of methane and ethane is 0.999133 through calculation, so that the natural gas leakage detection method has strong linear correlation, is different from other methane sources such as methane and the like, and provides a reference basis for distinguishing natural gas leakage.
Based on a mid-infrared continuous wavelength interband cascade laser and a 13m long optical path gas cell, a methane-ethane bi-component gas sensor was developed herein, covering 2989.033cm -1、2988.932cm-1、2988.795cm-1 methane absorption line and 2986.705cm -1 ethane absorption line. The dynamic detection experiment of the sensor is carried out by preparing methane gas samples with different volume fractions, the detection result is basically consistent with the concentration of the gas samples, and the average response time of the sensor is 3.9s. The sensor is used for respectively carrying out long-time performance test on gas samples with the volume fractions of 2ppm of methane and 10ppb of ethane, and the result shows that the average concentration value of methane is 2.01ppm and the average relative error is 0.5%; the average concentration of ethane was 10.18ppb and the average relative error was 1.8%. By Allan analysis of variance, the methane detection limit of the system at 1s is 18.1ppb; when the integration time is 327s, the lower methane detection limit of the system reaches the minimum value, which is 1.31ppb; when the integration time is 1s, the ethane detection lower limit is 1.06ppb; at an integration time of 402s, the minimum detection limit of ethane of the system is 0.02ppb, and the system has excellent detection performance and stability. In addition, a natural gas leakage source is simulated through mixed gas (the residual gas is N 2) of 1% methane and 0.1% ethane, a mobile monitoring experiment is carried out, a measurement result shows that methane and ethane have strong linear correlation, a pearson correlation coefficient is 0.999133 which is different from other methane sources such as methane and the like, and a reliable basis is provided for distinguishing natural gas leakage.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum is characterized by comprising the following steps of: the method comprises the following steps:
s1, selecting and measuring the absorption spectrum of methane and ethane in natural gas;
s2, constructing a methane and ethane detection system;
s3, analyzing the performance of the detection system;
S4, detecting natural gas leakage.
2. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 1, wherein the method comprises the following steps of: the specific value determination process of the absorption spectrum in the step S1 is as follows:
s1.1, determining an absorption line of 2ppm methane, 80ppb ethane and 2% water under different intensity pressure conditions;
s1.2, adopting a cascade laser between intermediate infrared continuous wavelength bands as a light source, and determining an absorption spectrum line;
s1.3, drawing images of methane, ethane and water spectral lines, and determining the optimal absorption spectral line.
3. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 1, wherein the method comprises the following steps of: the detection system comprises a middle infrared laser, a long-optical-path gas cell, a middle infrared photoelectric detector, a data acquisition card, a half-mirror and an etalon, wherein the laser comprises a current driving module and a temperature control module.
4. A method for synchronously measuring trace gas leakage of natural gas based on mid-infrared absorption spectrum according to claim 3, wherein: the system constructed in the step S2 specifically comprises the following working steps:
s2.1, performing current tuning on the laser through a current driving module, setting the center temperature of the laser by using a temperature control module, covering the methane and ethane absorption spectrum lines selected in the step S1, and emitting laser;
s2.2, emitting laser by a laser, and dividing the laser into two beams by a half-mirror;
S2.3, one beam passes through the etalon and then reaches the detector to realize the conversion of the relative frequency and the time domain of the light emitted by the laser, and the other beam of laser enters the long-path gas cell after being collimated, and the multiple reflection can reach 13m of effective optical path length and is absorbed by gas molecules to be detected;
s2.4, the mid-infrared photoelectric detector receives the transmitted light intensity after passing through the long-optical-path gas cell and converts the transmitted light intensity into a voltage signal;
S2.5, the data acquisition card processes the signals and calculates the gas concentration.
5. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 4, wherein the method comprises the following steps of: the performance analysis in step S3 includes the steps of:
s3.1, stability detection and lower limit detection;
s3.2, dynamic performance detection.
6. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 5, wherein the method comprises the following steps of: the stability test in step S3.1 and the lower limit test were carried out by measuring gas samples having a volume fraction of 2ppm methane and 10 ppb ethane for 30 minutes, respectively.
7. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 5, wherein the method comprises the following steps of: the specific steps of the dynamic performance detection in the step S3.2 are as follows:
s3.2.1, controlling the gas flow rate to be stabilized at 0.66L/min by using a gas distribution instrument;
S3.2.2, pumping methane gas samples grouped by different volume fractions into a long-path gas cell by a vacuum pump respectively;
s3.2.3, sequentially increasing the minimum volume fraction to the maximum volume fraction at the same group interval, and sequentially decreasing the maximum volume fraction to the minimum volume fraction at the same group interval to complete continuous dynamic measurement;
s3.2.3, analyzing the error.
8. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 1, wherein the method comprises the following steps of: the specific steps in the step S4 are as follows:
S4.1, continuously acquiring wind speed and wind direction data by using an anemograph, and carrying out surrounding running in a region with a leakage point;
S4.2, recording the position of the sensor in real time by using a global positioning system;
s4.3, recording methane and ethane concentration measurement values once per second, and synchronously calculating linear relation values of methane and ethane.
9. The method for synchronously measuring the trace gas leakage of the natural gas based on the mid-infrared absorption spectrum according to claim 8, wherein the method comprises the following steps of: the linear relation valueThe expression is as follows:
wherein/> Represents methane concentration measurements per second,/>Represents ethane concentration measurement per second,/>Represents the average value of methane concentration,/>The average value of ethane concentration is shown.
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